Ten crew members have been found dead and 14 have been rescued after two ships caught fire in the Kerch Strait near Crimea, Russia’s transport ministry said on Monday, with a rescue operation still underway.

The ministry said earlier on Monday that crew members were jumping into the sea to escape the blaze.

Both cargo ships were under the Tanzanian flag – Candy (Venice) and Maestro – and had a combined total of 31 crew members. Of them, 16 were Turkish citizens and 15 from India, it said. A search was underway for seven missing crew members.

An industry source told Reuters there were stormy conditions in the sea when the incident happened.

The Federal Agency for the Sea and River Transport said the blaze erupted while fuel was being pumped from one vessel to another.

The Kerch Strait between Russian-annexed Crimea and southern Russiacontrols access from the Black Sea to the Azov Sea, where there are both Russian and Ukrainian ports.

In November, Russia detained three Ukrainian navy vessels and their crews in the Black Sea near the Kerch Strait, fuelling tensions between the two countries. Russia annexed Crimea from Ukraine in 2014.